Effects of serotonin and carbachol on glial and neuronal rubidium uptake in leech CNS

Abstract

Effects of serotonin (5-HT) and carbachol on Rb uptake (used as a K marker) in leech neuron and glia were studied by electron probe microanalysis (EPMA). Hirudo medicinalis ganglia were perfused 60 s in 4 mM Rb substituted normal leech Ringer's with and without 5-HT (dosage range 5–500 μM) or carbachol (range 10–1000 μM), quench frozen, cryosectioned, and subjected to EPMA to determine elemental mass fractions and cell water content. Both 5-HT and carbachol altered leech neuron and glial cell elemental distribution and water content. In glial cells, a dose-dependent increase in Rb uptake was observed following 5-HT (control: 26 ± 2 μM; 5 μM: 47± 4; 50 μM: 62 ± 4; 500 μM: 82±11 mmol/kg dry wt. ± S.E.M.) and carbachol (10 μM: 35±3; 100 μM: 52±3; 1000 μM: 68±3 mmol/kg dry w wt. ± S. E. M.). In neurons, 5-HT and carbachol had small effects. 5-HT decreased glial and neuronal cell water content. Carbachol decreased neuronal (but not glial) water content by approximately the same amount (mean decrease 9%) regardless of dose. Both 5-HT and carbachol affected glial cell K-accumulating properties, providing evidence that certain neurotransmitters may modulate invertebrate glial cells' K clearance function.